Formation of transition-metal-based ohmic contacts to n-Mg2Si by Plasma Activated Sintering
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1044-U09-16
Formation of transition-metal-based ohmic contacts to n-Mg2Si by Plasma Activated Sintering Yohei Oguni1, Tsutomu Iida1, Atsunobu Matsumoto1, Takashi Nemoto2, Junichi Onosaka1, Hironori Takaniwa1, Tatsuya Sakamoto1, Daisuke Mori1, Masayasu Akasaka1, Junichi Sato2, Tadao Nakajima2, Keishi Nishio1, and Yoshifumi Takanashi1 1 Department of Materials Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba, 278-8510, Japan 2 Nippon Thermostat Co., Ltd., 6-59-2 Nakazato, Kiyose-shi, Tokyo, 204-0003, Japan ABSTRACT Electrode materials consisting of Cu, Ti and Ni were formed on Bi-doped n-type Mg2Si by means of a monobloc plasma-activated sintering (PAS) technique. Due to the difference in thermal expansion coefficients between Ti and Mg2Si, rather high residual thermal stresses gave rise to the introduction of cracks, which were mainly located in the Mg2Si layer, when Ti was used as the electrode material. In the case of the Cu electrodes, monobloc sintering could not be performed in a reproducible manner because Cu melts abruptly and effuses at around 973K, which is 100 K lower than the sintering temperature that is required for Mg2Si of good crystalline quality. When compared with the results for Cu and Ti, the monobloc PAS process for Ni was both stable and reproducible. The room-temperature I-V characteristics of Ni electrodes were considered to be adequate for practical applications, with durable Mg2Si-electrode junction properties being realized at a practical operating temperature of 600 K with ∆ T = 500 K. The highest open circuit voltage (VOC) observed was 41 mV at ∆T = 500 K (between 873 K and 373 K) for Ni electrodes fabricated using the monobloc PAS process. The voltage (V) and current (I) values with a 10 Ohm load were ~ 48 mV and ~ 2 mA at ∆T = 500 K. INTRODUCTION To assist in the reduction of the ‘Greenhouse Effect’, demands for a reduction in the global use of fossil fuels have been increasing. The automobile industry will continue to produce fossil-fuel based power sources for the next few decades, due to the increasingly heavy demands to motorize BRICs countries. A hybrid system comprising of an electric motor and a conventional engine is of interest, but this will not be sufficient to sustain the current huge demand for automobiles. Until the introduction of a hydrogen-based automobile, such as an ‘electric automobile’ which uses a fuel cell or hydrogen engine, one alternative solution is believed to be a drastic curtailment of fossil fuel consumption, namely, by a remarkable increase in the energy conversion efficiency of combustible power generators in order to maintain the sustainability of economically-growing societies. We have been focusing on a direct thermal-to-electric (TE) energy conversion technology using environmentally-benign TE materials that can be used in the mid-temperature range, such as in automobile and in SOFC fuel-cell applications. Magnesium silicide (Mg2Si) is a likely candidate for use as a TE material at operating temperatures ranging fr
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